Impelled by environmental concerns and increasing governmental regulations on the volatile organic content of inks and coatings, the applications of water-based flexographic and rotogravure inks are increasing in the ink industry. A typical water-based ink system is formulated by the addition of a binder resin (usually acrylic polymer latices) to a grind base. Grind bases are prepared by grinding pigments with alkali soluble grind resins (such as low molecular weight rosin-based resins or acrylic resins) until submicron particle size dispersions are obtained.
The use of wetting agents (i.e. grinding aids) help maximize mill-throughput by reducing grind times while also improving the gloss, stability, and color strength of pigment dispersions. High color strength allows dilution of finished inks to lower pigment levels. As pigment expense usually constitutes about two-thirds of the total cost of an ink, color strength remains a primary consideration for ink formulators.
An ink formulator must also consider the compatibility of the various ink components when selecting the grind resins or grinding aids to be used. Grind bases (i.e. pigment dispersions) are let-down with a variety of alkali-soluble resins or alkali-insoluble resin emulsions to achieve the properties desired for the end use of the ink. As wetting agents tend to be selective with pigments and ink types, often the grind resins and the letdown resins are not compatible. This incompatibility can result in pigment flocculation and flotation, viscosity increase, loss of adhesion and color strength, and other problems.
To minimize these problems "resinless" high solids pigment dispersions prepared with 5-10% dispersant are used in many cases. Pigments are ground with a low dosage of surfactant blends often referred to as "universal pigment dispersants." However, pigments such as titanium oxide, carbon black, and certain organic pigments have hydrophilic/lipophilic balance (HLB) values between 8 and 16; hence no one compound can give optimum performance. Therefore, blends are generally formulated to cover the whole HLB range in question.
Grinding aids which form high solids pigment dispersions help reduce shipping costs. The high solid pigment grinds are transported to the various ink formulators where the grinds are let-down into inks. At the press-site the inks are diluted to the needed press-ready viscosities and color strengths.
Therefore, it is the object of this invention to have a versatile pigment grinding aid for water-based ink formulations which allow high solids pigment dispersions to be obtained while maintaining excellent physical properties in the finished inks.